I just kreemed a tank that I modified... it had been coated badly by the PO.
This is what I learned:
1. POR and Kreem are the samething. But POR15 comes with a little more of the fluoroelastic polymer part, so is easier to use.
2. What every you do, don't let the tank dry out after the final rinse... it will flash rust and you won't get proper adhesion.
3. Give it two coats... I found my first coat very thin in areas, and I've seen tank liners flake up in the thin areas.
I'm not sure about POR15, but my 5gal tank needed two bottles of the Kreem liner part in order to give it two coats. You can buy them separately. When you are doing the final rinse, just pour the MEK in and swish it about quickly, pour it back in the container (use a funnel) and then pour the liner in right away. If you don't have a respirator, get one... MEK is nasty stuff. Even if you're outdoors, the fumes will get you.
As for removing the old liner, it turned out to be harder than I thought. I did several soaks with acetone and lengths of chain. I soaked for 24hr periods, shaking the tanks around now and then. A lot of the old liner came out, but where ever the coating was thick, it stayed. After the etching step of Kreem, much of the remaining liner came out, but there were still patches. I decided to kreem over this. It's been fine so far, we'll see how it holds up over the long haul.